The disclosure of Japanese Patent Application No. 2001-14790 filed on Jan. 23, 2001, and Japanese Patent Application No. 2001-60324 filed on Mar. 5, 2001 including the specification, drawings and abstract are incorporated herein by reference in their entireties.
1. Field of Invention
The invention relates to a running condition control system for a motor vehicle, which controls a vehicle""s running condition when the vehicle slips or creeps backward on an ascending road, especially when an operator of the vehicle changes his or her foot position from a brake pedal to an accelerator pedal.
2. Description of Related Art
There is known a technique for automatically applying a braking force to a wheel of a motor vehicle, when the vehicle is slipping backward on an ascending road upon a change in a foot position, of an operator of the vehicle, from a brake pedal to an accelerator pedal. For example, JP-A-10-16745 discloses such a technique, in which the braking force acts on the wheels, when it is detected that the vehicle is slipping backward contrary to a forward driving operation selected by the operator, so that a speed of the backward slipping of the vehicle is decreased. The disclosed technique controls an amount of the braking force acting on the wheels so that the backward slipping speed of the vehicle does not exceed a predetermined upper limit. Therefore, the backward slipping speed of the vehicle is held within a constant range. However, in the disclosed technique, the magnitude of the braking force acting on the wheels is based upon the speed at which the vehicle is slipping backward and does not depend on the rate of increase of the backward slipping speed, i.e., acceleration, of the vehicle. Therefore, in the above case, the backward slipping speed of the vehicle may not be decreased sufficiently where the backward slipping speed of the vehicle is increasing at a high rate.
Further, a continuous execution of the braking force control upon backward slipping of the vehicle may mislead the operator into thinking that the controlled backward slipping speed is a natural backward slipping speed of the vehicle. The control for decreasing the backward slipping speed of the vehicle was originally adapted to operate when, for example, the operator changed his or her foot position from the brake pedal to the accelerator pedal to temporarily assist the operator in the intended operation. For the above reason, the control is required to cause the operator to appropriately operate the brake and accelerator pedals, while assisting the operator in operating them.
There is known a brake actuator used in a traction control system for limiting the slipping of the wheels during acceleration, or a turning behavior control system which applies a braking force to a predetermined wheel of the vehicle. The known brake actuator may be utilized for temporarily applying the braking force to the wheels in order to reduce the backward slipping speed of the vehicle. However, if the control system for decreasing the backward slipping speed of the vehicle is utilized for a longer period of time, an enhanced and more durable actuator would be required.
It is one object of the invention to provide a running condition control system for a vehicle, which is capable of inducing an operator of the vehicle to appropriately operate a brake pedal and an accelerator pedal, while assisting the operator in operating the vehicle when starting the vehicle on an ascending road.
It is another object of the invention to provide a running condition control system for a motor vehicle, which is capable of more effectively decreasing the speed at which the vehicle is slipping backward on the ascending road depending on a tendency of the vehicle to slip backwards.
To accomplish the above and/or other objects, one aspect of the invention provides a running condition control system for controlling a braking force applied to the wheels of the vehicle when an actual running direction of the vehicle is contrary to a running direction in which the vehicle is intended to run, in accordance with an operation selected by an operator of the vehicle. The running condition control system includes a vehicle operation state detector that determines whether the operation of the operator is a forward driving operation or a reverse driving operation, an actual running direction detector that detects an actual running direction of the vehicle, a braking device that applies the braking force to a predetermined wheel apart from a braking operation performed by the operator; and a controller that controls the braking device to apply the braking force to a wheel which rotates in the same direction as the actual running direction of the vehicle when the intended running direction of the vehicle, which is determined by the operation state detector, is contrary to the actual running direction of the vehicle detected by the actual running direction detector, and stops the braking device from applying the braking force when the braking device has been continuously controlled for a first predetermined period of time.
The controller controls the operation of the braking force applying device such that, when the operator""s intended driving direction and the actual running direction of the vehicle are contrary to each other, that is, when the vehicle is slipping backward on the ascending road, the braking force is applied to a wheel rotating in the direction in which the vehicle is slipping backward. Thus, the backward slipping speed of the vehicle can be decreased. The controller terminates the control operation executed by the controller, when the controller has executed its control operation for a period in excess of the predetermined period of time. This arrangement is effective to induce the operator to operate the brake and accelerator pedals, while avoiding a continuous operation of the braking device for a long period of time and ensuring protection of the braking device.
In the running condition control system, when the braking force is continuously controlled for a period of time that is larger than a second period of time that is set smaller than the first period of time, the braking force applied to the wheel is reduced gently.
In the running condition control system, the controller decreases the pressure of the braking force such that the braking force applied to the wheel decreases along a gentle gradient instead of immediately terminating the braking force. This arrangement prevents a sudden change in the backward slipping speed of the vehicle, and makes it possible to notify the operator that the control for decreasing the backward slipping speed of the vehicle is being terminated. Accordingly, this arrangement provides a sufficient time for the driver to depress the brake pedal and/or the acceleration pedal.
In the running condition control system, the controller controls the magnitude of the braking force applied to the wheel, wherein the magnitude of the braking force applied is changed in accordance with the magnitude of the acceleration of the vehicle in the actual running direction.
In the running condition control system, the controller controls distribution of the braking force applied to the wheels located on an upper side of an inclined road and to the wheels located on a lower side of the inclined road such that the braking force applied to the wheels located on the lower side of the inclined road increases as a gradient of the inclined road becomes higher.
In the running condition control system including a rotating direction detector that detects a rotating direction of each of the wheels of the vehicle, the controller applies a first braking force to at least one wheel rotating in a direction that is contrary to the running direction intended by the operator, which is detected by the rotating direction detector, and applies a second braking force to at least one wheel rotating in a direction that is the same as the running direction intended by the operator, apart from a braking operation performed by the operator, the first braking force applied to the at least one wheel rotating in the direction that is contrary to the running direction intended by the operator is determined depending upon a running state of the vehicle; and the second braking force, applied to the at least one wheel rotating in the direction that is the same as the running direction intended by the operator, is determined depending upon the rotating state of the wheel.